Lab 6 Bone Investigations Flashcards
Where is 99% of calcium stored?
Bone and teeth
How much of plasma calcium is free ionized calcium?
50%
Biologically active form
How much of plasma calcium is protein-bound calcium?
40%
How much of plasma calcium is complexed calcium?
10%
Bound to albumin/globulin
What anticoagulant can be used in plasma/serum when measuring calcium?
Lithium heparin
What is corrected calcium?
Used to adjust the total calcium concentration for changes in albumin levels.
Albumin is the main protein that binds calcium in the blood.
If albumin levels are low, the total calcium concentration will be low.
What happens to calcium concentration if albumin levels are low
Total calcium concentration is also low.
3 regulators of calcium concentration
- Parathyroid hormone
- Calcitonin
- Vitamin D
Hypocalcaemia - causes (5)
Serum/plasma calcium levels below ref range.
1. Decreased GI absorption (vit D deficiency)
2. Increased renal loss
3. Decreased bone loss (Hypoparathyroidism)
4. Decreased albumin levels
5. EDTA contamination.
Symptoms of hypocalcinaemia
Neurological symptoms (seizures, tetany)
Cardiovascular symptoms
Cataracts
Hypocalcinaemia treatment
Oral calcium supplements
Vitamin D supplements
Treat underlying cause
Hypercalcaemia - causes (4)
Serum/plasma calcium levels above ref range
Caused by
1. Increased GI absorption
2. Decreased renal loss
3. Increased bone loss (hyperparathyroidism)
4. Increased albumin levels.
Clinical features of Hypercalcaemia
Neurological symptoms (confusion, lethargy, coma)
Cardiovascular symptoms (arrhythmias)
GI symptoms (constipation, anorexia, nausea)
Renal symptoms (polyuria, polydipsia)T
Treatment of hypercalcaemia
IV fluids
Biphosphonates
Treat underlying cause
Components of the Bone profile
- Total calcium
- Phosphate
- Alkaline phosphatase
- Albumin
- Corrected calcium (derived from total calcium + albumin)
What is alkaline phosphatase (ALP) a marker of?
= Bone formation
May be elevated in bone disease
i.e. increased bone turnover (process of resorption followed by replacement by new bone).
What do phosphate levels indicate in bone profile?
Changes in phosphate levels reflect changes in calcium deposition or resorption in bone
- often have reciprocal relationship i.e. increased calcium mean decreased phosphate.
How does parathryoid hormone affect calcium/phosphate levels?
Increases calcium
Decreases phosphate
Causes of reduced GI absorption of calcium
- Vitamin D deficiency
- Malabsorption e.g. coeliacs disease, crohns disease
How does vitamin D deficiency affect calcium levels?
Vit D required for calcium absorption in intestines.
Deficiency leads to reduced calcium absorption.
Leads to reduced bone resorption.
Can lead to osteomalaice/rickets.
What is osteomalaice/rickets
Softening of bones due to defective mineralization.
Leads to bone pain, bone deformities, fractures.
Main cause of osteomalaice/rickets
Vit D deficiency
How does defective kidney/renal failure lead to hypocalcaemia?
- Cannot hydroxylate vitamin D to active form - cannot reabsorb calcium in the kidneys.
- Vit D deficiency leads to reduced GI absorption of calcium also.
- Vit D deficiency leads to reduced bone resorption.
- Diseased kidney may not respond to PTH causing it to be overproduced -> stimulates bone resorption.
How does hypoparathryoidism cause hypocalcaemia?
Decreased PTH production by parathyroid glands leads to decreased stimulation of bone resorption.
What is bone resorption
The process by which osteoclasts break down bone tissue releasing minerals such as calcium and phosphate into bloodstream.
Stimulated by parathyroid
Critical for maintaining calcium balance
What is hungry bone syndrome
Parathyroidectomy leads to rapid uptake of calcium into bones leading to hypocalcaemia
Causes of hypercalcaemia
- Primary hyperparathyroidism - overactive parathyroid produces excess PTH = increased calcium release from bone + increased renal calcium reabsorption.
- Malignancy - PTH-related peptide produced by some tumors mimics PTH leading to increased calcium.
Causes of hypocalcaemia
- Hypoparathyroidism = low PTH - decreased bone resorption and renal calcium reabsorption.
- Vitamin D deficiency - reduced intestinal calcium absorption (leads to rickets/osteomalaice)
- Chronic Kidney disease - decreased vit D activation
ALP in bone profile
ALP is an enzyme found in bones and is used to assess bone metabolism and bone turnover
What does high ALP indicate + causes?
Increased bone turnover due to bone formation/breakdown
Causes:
1. Osteomalaice + rickets
2. Hyperparathryoidism
3. Fractures + bone healing
4. Seen in children + adolescents (due to active bone growth)
5. Increased in liver disease!!!
What does low ALP indicate and its causes?
Indicates low bone turnover or metabolism issues
1. Severe malnutrition
2. Vit D deficiency
